Acid reflux
I had horrible reflux after my surgery and had to try various prescription PPIs before hitting on one that worked and one that I wasn't allergic to. Protonix 40mg per day does the trick for me.
Lifestyle changes you can try too: absolutely NO eating at least 60 minutes or more before lying down; steer clear of acidy foods like coffee and tomatoes; sleep with upper body propped up or head of bed propped up; avoid peppermint (it relaxes the esophageal sphincter and allows food to get up in the esophagus).